Hello,

As I didn't get an answer on povray.newusers maybe it is a advanced problem:

I have a problem using Photons to simulate a laser beam which is reflected
by a mirror. Please take a look at the povray example at the end of this
message. If you calculate the example, you will notice that the reflected
laser beam does not start at the point where the incomming beam hits the
mirror, but somewhere above the mirror, this looks not very natural. What
is wrong with my example?

And second question, how can I achieve that the reflected beam is not so
much scattered?

Thanks in advance for your answers,
Peter

---------------------------------------
help.pov:
---------------------------------------

global_settings {
   adc_bailout 0.0039216
   assumed_gamma 1.5
   noise_generator 2

   photons {
      count 2000
      gather 40, 100
      media 100, 2
   }
}

camera {
   perspective
   location <0, 5, -5>
   sky <0, 1, 0>
   direction <0, 0, 1>
   right <1.3333, 0, 0>
   up <0, 1, 0>
   look_at <5, 0, 0>
}

light_source {
   <4, 5, -5>, rgb <1, 1, 1>
   media_interaction off
   media_attenuation off
}

light_source {
   //*PMName Light
   <0, 0, 0>, rgb <1, 1, 1>
   cylinder
   radius 0.3
   falloff 0.3
   tightness 0
   point_at <8, 0, 0>

   photons {
      refraction on
      reflection on
   }
}

box {
   //*PMName Interior
   <0, -4, -4>, <8, 4, 4>

   pigment {
      color rgbft <0, 0, 0, 1, 1>
   }

   interior {
      media {
         method 3
         intervals 1
         ratio 1

         scattering {
            1, rgb <1, 1, 1>
            extinction 0
         }
      }
   }
   scale 1
   rotate <0, 0, 0>
   translate y*0.5
   hollow
}


union {
   //*PMName Mirror

   box {
      <-0.1, -1, -1>, <0.1, 1, 1>

      pigment {
         color rgb <0.188235, 0.188235, 0.188235>
      }
   }

   box {
      //*PMName MirrorPiece
      <-0.101, -0.5, -0.5>, <0.101, 0.5, 0.5>

      pigment {
         color rgb <0.701961, 0.52549, 0.384314>
      }

      finish {
         ambient rgb <0, 0, 0>
         diffuse 0

         reflection {
            rgb <1, 1, 1>
         }
      }

      photons {
         target
         refraction on
         reflection on
         collect off
      }
   }
   rotate z*135
   translate x*6
}

Post a reply to this message

"Peter T. Mayer" <nomail@nomail> wrote in message 
news:web.41ecc9f82fb492d1173073970@news.povray.org...
> laser beam does not start at the point where the incomming beam hits the
> mirror, but somewhere above the mirror, this looks not very natural. What
> is wrong with my example?
>
> And second question, how can I achieve that the reflected beam is not so
> much scattered?

Hiya. Stumbling across your question here, hopefully I'll have the right 
answer.

Probably only a matter of adding a samples value so try that to prevent 
missing or artifact prone media. Oftentimes it needs to be 50 or more-- slow 
as that may be. At least I don't believe raising max_trace_level would help 
since this is only a few surfaces.

As to the scatter, well, it could be that you need to increase 'tightness' 
of your laser light. You might try using the 'parallel' keyword, too, 
although I don't think this will change anything in this scene as it is now.

I've rendered your script and tried a few things. Looks like that frame 
around the mirror could be confused as incorrect media appearance too, but 
what happens is that the illuminated media only seems brighter with that 
behind it. The grayness against the blackness makes a brightness change. 
However, media samples 100 really helps (photons part left the same).

Bob H.

Post a reply to this message

"Bob Hughes" <omn### [at] charternet> wrote:

> Hiya. Stumbling across your question here, hopefully I'll have the right
> answer.
>
Thank you for your answer, the solution works well.

Nevertheless I m not very satisfied with the result. If you look at the the
original beam you can see, that he is slightly transparent, not so the
reflected beam.

Thanks,
Peter

Post a reply to this message